Wetting agents for electroplating baths



United States Patent 3,d34,ill WETTPLNG AGENTS FQR ELECTRQPLATENG BATE-ES Wennemar Strauss, Dusseldort-Holthausen, and Rudi Hayden, Dusseldorf, Germany, assignors to Dehydag Deutsehe Hydrierwerke G.m.b.ld., Dusseldorf, Germany, a corporation of Germany No Drawing. Filed Apr. 20, 1959, ger. No. $07,2S Claims priority, application Germany Apr. 24, 1958 illaims. (El. 204--51) This invention relates to additives for electroplating baths and to a process and a bath for electroplating making use of such additives. It more specifically relates to the addition of organic phosphoric acid ester derivatives to electroplating baths as wetting and porosity preventing agents.

lit is known to add wetting agents to electroplating baths for the production of nickel, copper or zinc electroplates. 'lhese additives have the effect that the hydrogen which forms at the cathode during the electroplating process is released rapidly and as completely as possible. It the hydrogen remains on the cathode material for longer periods of time it causes an undesirable pore formation in the metal electroplates.

The prevention of pore formation is of great importance in the electroplating art in view of the desired corrosion resistance of the metal electroplates. Another task of the wetting agents is to prevent the electrophoretic deposition of small particles of impurities on the metal surfaces, because the corrosion resistance also sufiers from the inclumium baths.

quantities of oxygen and hydrogen released in the chromiurn baths due to the poor current output do not escape in the form of fogs, but that instead a foam cover forms on the bath liquid. This measure prevents considerable losses in relatively expensive chromium bath liquid due to continuous removal of the fog by suction, so that in many instances the suction removal of the bath fog can be entirely omitted.

Despite the great number of known wetting agents the selection of operative substances for electroplating purposes is relatively small. Thus, alkylsulfonates, alkylsulfates and aralkylsulfonates or sulfates are preferably used in nickel electroplating baths, while in the field of acid and cyanide preliminary copper-plating alkyl-polyglycol ethers are employed. Periiuoro-alkylsulfonates are known to be stable wetting agents for chromium baths.

it is an object of this invention to provide wetting agent additive compounds for electroplating baths which have a high degree of stability.

It is a further object to provide additive compounds which prevent vaporization and loss of the electroplating bath solution.

it is a further object to provide wetting agents which may be used in acid, alkaline or cyanide electroplating baths to produce deposits of the Well known plating metals.

Another object is to provide electroplating processes and baths wherein electrodeposits may be obtained which are free from pores and inorganic impurities.

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now found that acid alkyland aralkyl-phosphoric acid esters as well as alkylpolyglycolether-phosphoric acid esters or their salts may be used with advantage in a variety of electroplating baths. In addition to their good wetting properties, these compounds have the advantage over the corresponding sulfonates or sulfates that they are considerably more stable in the baths. Fur- "ice ther, they have the advantage over the alkylpolyglycol ethers that they do not have a turbidity point and are not salted out even in hot cyanide copper-plating baths. The phosphoric acid esters even have brightening properties in cyanide baths. In chromium-plating baths, especially the alkylphosphates exhibit excellent stability properties, so that they may be used in place of the expensive and difficult-to-prepare perfiuorinated organic sulfonic acids.

Examples of compounds of the claimed type are the acid monoor diphosphoric acid esters of octyl, decyl, dodecyl, octadecyl or octadecenyl alcohol, or of hexyl, octyl or dodecyl phenol and their water-soluble salts, as well as the phosphoric acid esters of alkylpolyglycol ethers having the general structural formula wherein 11:8 to 20 and m=0 to 50, and X is hydrogen or an inorganic or organic base.

The wetting agents may be used in acid, cyanide or alkaline baths for the production of copper, nickel, chromium, zinc, cadmium, tin, brass, bronze, gold and silver electroplates. They are added to the baths preferably in amounts from 0.01 to 5 grn./liter. The electroplating bath is carried out at bath temperatures from room temperature to 60 0., and up to C. for alkaline baths; and at current density ranges from 0.5 ampjdm. to 16 amp./dm. and up to 40 arnp./dm. fior alkaline baths.

The following examples have been set forth to enable persons skilled in the art to better understand and practice our invention. However, it will be understood that there is no intention on our part of limiting our invention to these examples.

Example I When 0.01 to 0.2 gm./liter dodecyl-phosphoric acid ester was dissolved in a cyanide copper bath containing gm./liter copper cyanide, 12S gm./liter sodium cyanide and 30 gm./ liter sodium hydroxide, and objects made of iron or steel were electroplated therein between 60 and 80 C. in a current density range of about 1 to 6 amp/din pore-free copper electroplates were obtained. These electroplates are haracterized over those which were obtained without the alkylphosphate additive and under otherwise identical conditions by a distinctly finer grain structure.

Example 11 0.02 to 0.1 gm./liter octyl-phosphoric acid ester was dissolved in a bright chromium-plating bath containing 290 gm./liter CrO When bright nickel-plated objects were chromium-plated in this bath at current densities of 10 to 20 amp/din. and 35 to 40 C., a foam cover of a thickness of about 1 to 2 cm. formed on the bath, which completely prevented the occurrence of chromic acid fogs. The chromium electroplates turned out full-bright.

Example 111 When an acid copper bath, which contained 0.25 gm./liter N,N-diethyl-dithiocarbamic acid-n-propyl ester w-sodium sulfonate and 2 gm./liter l-diethylarnino-3- chloropropanol-Z as brightening agents in addition to 200 gm./liter CuSO jl-l O and 60 gm./liter H 80 was modified with 0.01 to 0.3 gm./liter of the compound C12'H25O(CH2CH2O)'1 CH CH C'PO Na and ir-Oll or brass objects were electroplated in this bath within a current density range ofi 0.5 to 7.5 amp./dm. full-bright copper elect-roplates completely free from pores were obtained.

While we have disclosed certain specific embodiments and preferred modes of practice of our invention, it will be understood that we do not intend to be limited thereby and various changes and modifications may be made withthe phosphoric acid ester water soluble.

2. The bath of claim 1 wherein the additive compound is dodecyl phosphoric acid ester.

3. The bath of claim 1 wherein the additive compound is octyl phosphoric acid ester.

4. The bath of claim 1 wherein the additive compound is a compound having the-formula:

C H O(CH CH O) CH CH OPO Na 5. A process and wherein Z is a radical having at least 8 carbon atoms selected from the group consisting of alkyl,

the phosphoric acid ester Watersoluble. V

6. The process of claim wherein the additive compound is dodecyl phosphoric'acid ester.

7. The process of claim 5 wherein the additive compound is octyl phosphoric acid ester.

8. The process of claim 5 wherein the additive compound is a compound having the formula C12H250(CH2CH20)7 CH CH OPO Na 9. A method for solution in the operation of electroplating baths which additive compound comprising a phosphoric acid ester having a structural formula selected from the group con sisting of:

Z-PO X and POzX -0 wherein Z is a radical having at least 8 carbon atoms selected from the group consisting of alkyl, alkylaryl and consisting of hydrogen and cations capable of rendering the phosphoric acid ester water soluble.

110. A method for preventing vapor losses of bath solution in the ZPO X and wherein Z is a. radical having at least 8 carbon atoms selected from the group consisting of alkyl, alkylaryl and polyglycolether radicals, and X is selected from the group consisting of hydrogen and cations capable of rendering the phosphoric acid ester water soluble.

References Cited in the file of this patent UNITED STATES PATENTS Foulke et al. June 17, 1958 Gundel et al June 30, 1959 Haas et a1. July 7, 1959 

1. AN ELECTROPLATING BATH FOR PRODUCING ELECTRODEPOSITS OF METALS CAPABLE OF BEING ELECTRODEPOSITED COMPRISING AN AQUEOUS SOLUTION OF AN INORGANIC SALT OF THE METAL TO BE DEPOSITED AND 0.01 TO 5 GM./LITER OF AN ADDITIVE COMPOUND COMPRISING A PHOSPHORIC ACID ESTER HAVING A STRUCTURAL FORMULA SELECTED FROM THE GROUP CONSISTING OF: 